Field of the Invention
The present invention relates to an image forming apparatus including a fixing unit to fix an unfixed toner image onto a recording medium. To be more specific, the invention relates to an image forming apparatus including a fixing unit which is configured to change strength of a pressing force between two nip members (rollers, for example) forming a fixing nip.
Related Art
Heretofore, some image forming apparatuses are configured to change strength of a pressing force between nip members which form a fixing nip. Depending on types of a recording medium to be used, a preferable pressing force at the fixing nip differs. In one example of an image forming apparatus, there set two levels of strength of the pressing force. The stronger pressing force is adopted for a plain paper and the weaker pressing force is adopted for special recording media including an envelope. An image forming apparatus in another example is configured to switch the pressing force as similar to the above example so that the image forming apparatus is not entered into a delivery stage under the strong pressing force.
Patent Document 1 discloses one example of a fixing device configured to switch the pressing force. The fixing device of Patent Document 1 includes “a switching member” to switch the press-contact condition of “a fixing roller.” The switching member is configured to be in three positions of “a copying position,” “a jam clearing position,” and “a press-contact releasing position for delivery.” The fixing roller is under press-contact state in the copying position and released from press-contact state in the jam clearing position and in the press-contact releasing position for delivery. The image forming apparatus is provided with a cover to close and open for coping with a paper jamming. This cover can be closed in the copying position and in the press-contact releasing position for delivery, but cannot be closed in the jam clearing position. When the cover is closed while the switching member is in the press-contact releasing position for delivery, the fixing roller at a delivery stage is free from pressing.